The present invention relates to a nonaqueous electrolyte secondary battery and a method of manufacturing the nonaqueous electrolyte secondary battery.
Recently, a thin lithium ion secondary battery has been put on the market as a nonaqueous electrolyte secondary battery for portable apparatuses such as portable phones. This battery uses lithium cobalt oxide (e.g., LiCoO2) as a positive electrode active material, a graphite material or carbonaceous material as a negative electrode active material, an organic solvent in which a lithium salt is dissolved as an electrolyte, and a porous film as a separator.
Although it is being demanded to decrease the thickness of batteries to meet decreasing thickness of portable apparatuses, thin lithium ion secondary batteries 4 mm or less in thickness are difficult to put to practical use. Therefore, a card-type lithium secondary battery using a polymer electrolyte has been conventionally proposed and developed to be commercially practical.
A lithium secondary battery using a polymer electrolyte, however, contains a gelled polymer holding a nonaqueous electrolyte. Hence, this lithium secondary battery has larger electrode interface impedance and lower lithium ion conductivity than those of a lithium secondary battery using a nonaqueous electrolyte. Also, the thickness of the polymer electrolyte should be increased compared with the separator to raise its strength, and as a result the energy density lowers.
Accordingly, a lithium secondary battery using a polymer electrolyte is inferior, in volume energy density, cycle life and large discharge characteristic, to a thin lithium secondary battery impregnated with a nonaqueous electrolyte in a solution or liquid form.
The scope of claims of Jpn. Pat. Appln. KOKAI Publication No. 10-177865 describes a lithium ion secondary battery including a positive electrode, a negative electrode, a separator which have opposing surfaces holding an electrolyte in place, and an adhesive resin layer which is made from a mixed phase of an electrolyte phase, a polymer gel phase containing an electrolyte, and a polymer solid phase and adheres the positive and negative electrodes to the opposing surfaces of the separator. The scope of claims of Jpn. Pat. Appln. KOKAI Publication No. 10-189054 describes a lithium ion secondary battery manufacturing method including the steps of coating a separator with a binder resin solution prepared by dissolving polyvinylidene fluoride as a main component in a solvent, putting an electrode on this separator and drying these materials, as they are adhered to each other, to evaporate the solvent and thereby form a battery stacked body, and impregnating this battery stacked body with an electrolyte. Also, the scope of claims of Jpn. Pat. Appln. KOKAI Publication No. 10-172606 describes a lithium ion secondary battery including a positive electrode, a negative electrode, a separator inserted between the positive and negative electrodes and holding an electrolyte containing lithium ions, and a porous adhesive resin layer for holding the electrolyte and adhering the positive electrode, negative electrode, and separator.
Unfortunately, the lithium ion secondary batteries disclosed in these patent publications have high internal resistance and are therefore inferior in cycle life and large discharge characteristic.
It is an object of the present invention to provide a nonaqueous electrolyte secondary battery in which an electrode group is impregnated with a nonaqueous electrolyte in a solution or liquid form, and which has an improved large discharge characteristic and cycle characteristic and can be made thin.
It is another object of the present invention to provide a nonaqueous electrolyte secondary battery manufacturing method capable of improving the large discharge characteristic and cycle characteristic and decreasing the thickness of a nonaqueous electrolyte secondary battery in which an electrode group is impregnated with a nonaqueous electrolyte in a solution or liquid form.
It is still another object of the present invention to provide a nonaqueous electrolyte secondary battery in which an electrode group is impregnated with a nonaqueous electrolyte in a solution or liquid form, and which has an improved cycle characteristic and can be made thin.
It is still another object of the present invention to provide a nonaqueous electrolyte secondary battery manufacturing method capable of improving the cycle characteristic and decreasing the thickness of a nonaqueous electrolyte secondary battery in which an electrode group is impregnated with a nonaqueous electrolyte in a solution or liquid form.
It is still another object of the present invention to provide a nonaqueous electrolyte secondary battery having a reduced internal short circuit occurrence frequency and an improved large discharge characteristic and cycle characteristic.
According to the present invention, there is provided a nonaqueous electrolyte secondary battery comprising an electrode group comprising a positive electrode, a negative electrode, and a separator which is interposed between the positive electrode and the negative electrode and which contains a porous sheet whose air permeability is 600 sec/100 cm3 or less, a nonaqueous electrolyte with which the electrode group is impregnated, and a jacket for housing the electrode group, wherein the positive electrode and the separator are adhered to each other by adhesive polymers that are held in voids of the positive electrode and those of the separator, and the negative electrode and the separator are adhered to each other by adhesive polymers that are held in voids of the negative electrode and those of the separator.
According to the present invention, there is provided a nonaqueous electrolyte secondary battery comprising an electrode group comprising a positive electrode, a negative electrode, and a separator for separating the positive and negative electrodes from each other, a jacket for housing the electrode group, and a nonaqueous electrolyte with which the electrode group is impregnated, wherein the positive electrode and the separator are adhered to each other by adhesive polymers that are dispersedly present in the positive electrode and the separator and in a boundary between the positive electrode and the separator, and the negative electrode and the separator are adhered to each other by adhesive polymers that are dispersedly present in the negative electrode and the separator and in a boundary between the negative electrode and the separator.
According to the present invention, there is provided a nonaqueous electrolyte secondary battery comprising an electrode group having a structure formed by spirally winding a positive electrode and a negative electrode with a separator interposed between them and compressing a resultant coil in a direction of diameter, a nonaqueous electrolyte with which the electrode group is impregnated, and a film jacket in which the electrode group is housed, and a surface of the electrode group to which a stacked structure is exposed has a shape meeting:
0.9xe2x89xa6L2/L1xe2x89xa61.2xe2x80x83xe2x80x83(I)
wherein L2 is a thickness of a most multilayered portion in a region of the surface except curved-layer-regions and L1 is a thickness of an end portion which is one of end portions of the region except the curved-layer-regions and is equal in number of layers to L2.
According to the present invention, there is provided a nonaqueous electrolyte secondary battery comprising an electrode group having a structure formed by folding a positive electrode and a negative electrode twice or more with a separator interposed therebetween, a nonaqueous electrolyte with which the electrode group is impregnated, and a film jacket in which the electrode group is housed, and a surface of the electrode group to which a stacked structure is exposed has a shape meeting:
0.9xe2x89xa6L4/L3xe2x89xa61.2xe2x80x83xe2x80x83(II)
wherein L4 is a thickness of a most multilayered portion in a region of the surface except folded-layer-regions and L3 is a thickness of an end portion which is one of end portions of the region except the folded-layer-regions and is equal in number of layers to L4.
According to the present invention, there is provided a nonaqueous electrolyte secondary battery comprising an electrode group having a structure formed by spirally winding a positive electrode and a negative electrode with a separator interposed therebetween and compressing a resultant coil in a direction of diameter, a nonaqueous electrolyte with which the electrode group is impregnated, and a film jacket in which the electrode group is housed,
wherein the positive electrode and the separator are adhered to each other by adhesive polymers that are dispersedly present in the positive electrode and the separator and in a boundary between the positive electrode and the separator, and the negative electrode and the separator are adhered to each other by adhesive polymers that are dispersedly present in the negative electrode and the separator and in a boundary between the negative electrode and the separator, and a surface of the electrode group to which a stacked structure is exposed has a shape meeting:
0.9xe2x89xa6L2/L1xe2x89xa61.2xe2x80x83xe2x80x83(I)
wherein L2 is a thickness of a most multilayered portion in a region of the surface except curved-layer-regions and L1 is a thickness of an end portion which is one of end portions of the region except the curved-layer-regions and is equal in number of layers to L2.
According to the present invention, there is provided a nonaqueous electrolyte secondary battery comprising an electrode group having a structure formed by folding a stack comprising a positive electrode, a negative electrode, and a separator not less than twice, a nonaqueous electrolyte with which the electrode group is impregnated, and a film jacket in which the electrode group is housed,
wherein the positive electrode and the separator are adhered to each other by adhesive polymers that are dispersedly present in the positive electrode and the separator and in a boundary between the positive electrode and the separator, and the negative electrode and the separator are adhered to each other by adhesive polymers that are dispersedly present in the negative electrode and the separator and in a boundary between the negative electrode and the separator, and a surface of the electrode group to which a stacked structure is exposed has a shape meeting:
xe2x80x830.9xe2x89xa6L4/L3xe2x89xa61.2xe2x80x83xe2x80x83(II)
wherein L4 is a thickness of a most multilayered portion in a region of the surface except folded-layer-regions and L3 is a thickness of an end portion which is one of end portions of the region except the folded-layer-regions and is equal in number of layers to L4.
According to the present invention, there is provided a nonaqueous electrolyte secondary battery comprising an electrode group comprising a stack comprising at least one positive electrode, at least one negative electrode, at least one separator, and at least two adhesive layers, one interposed between the positive electrode and the separator and another between the negative electrode and the separator, a nonaqueous electrolyte with which the electrode group is impregnated, and a film jacket in which the electrode group is housed, wherein the at least one separator contains 10 wt % or less (including 0 wt %) of an adhesive polymer, and an end portion of the separator protrudes compared with an end portion of the at least one positive electrode or an end portion of the at least one negative electrode.
According to the present invention, there is provided a method of manufacturing a nonaqueous electrolyte secondary battery, comprising the steps of forming an electrode group by interposing a separator between a positive electrode and a negative electrode, impregnating the electrode group with a solution in which an adhesive polymer is dissolved, molding the electrode group, and impregnating the electrode group with a nonaqueous electrolyte.
According to the present invention, there is provided a method of manufacturing a nonaqueous electrolyte secondary battery, comprising the steps of forming an electrode group by interposing a separator made from at least one type of material selected from polyolefin and cellulose between a positive electrode and a negative electrode, molding the electrode group while heating, and impregnating the electrode group with a nonaqueous electrolyte.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.